1. Field of the Invention
This invention relates to a control apparatus and control method of machine tools including grinding machines.
More specifically, it relates to an apparatus which automatically controls the change points of constant infeed speed for each workpiece by applying fuzzy reasoning.
Also, the invention relates to a method for automatically controlling the starting point of spark out in the plunge, traverse, taper, or shoulder grinding cycle for each workpiece by applying fuzzy reasoning.
Furthermore, this invention relates to an apparatus for automatically judging, by applying fuzzy reasoning, whether the change or makeup of coolant for machine tools including grinding machines is necessary.
Still furthermore, this invention relates to an apparatus for automatically judging, by applying fuzzy reasoning, whether truing or dressing of grinding wheels on grinding machines is necessary.
2. Description of the Related Art
In the conventional grinding cycle for cylindrical grinding machines, the change points of constant infeed speed of grinding wheel were fixed for the same types of workpieces in both cases of the change from rough grinding to fine grinding and the change from fine grinding to spark out. The spark out starting point means, for example in the plunge grinding cycle, the workpiece diameter at which the grinding wheel stops infeeding, and in the shoulder grinding cycle the workpiece width at which the grinding wheel stops infeeding.
The fixed infeed speed change points for a grinding wheel presents the following disadvantages:
(1) Shortening of machining time is limited. Particularly when the change point from rough grinding to fine grinding is fixed, the shortening is very restricted.
(2) Variations in quality occur.
(3) Variations in machining accuracy occur.
The reasons for these disadvantages are as follows:
(i) The grinding quality of the wheel, though being high immediately after dressing, is gradually degraded by glazing or loading.
(ii) When the infeed speed change points including the spark out starting point are fixed, the change point from rough to fine grinding or the change point from fine grinding to spark out is reached rapidly if the grinding quality of the wheel is high. Moreover, the time for attaining the finished dimensions (finished diameter or finished width) after the start of spark out is short, but infeeding may become excessive, and the finished dimensions cannot be obtained smoothly, which results in poor quality (surface roughness).
(iii) If the grinding quality of the wheel is low, the surface roughness is good, but same amount becomes left from cutting. Also, it takes longer to attain the finished dimensions.
(iv) Depending on the grinding quality of the wheel, excessive infeeding occurs or some portion of a workpiece becomes left out from cutting, resulting in variations in machining accuracy and variations in surface roughness. Therefore, the change points of constant infeed speed including the spark out starting point are set at a fixed position slightly larger than the usual position to obtain the finished diameter or finished width smoothly and also to prevent excessive infeed even when the grinding quality of the wheel is high.
(v) As a result, the machining time becomes longer and varies greatly as the grinding quality of the wheel degrades. If the grinding quality of the wheel is so poor that a large amount becomes left from cutting, an auxiliary pick is required; it takes further longer to attain the finished dimensions.
The adaptive control grinding on cylindrical grinding machines is also known as disclosed in Japanese Patent Publication No. 3951/1985 (60-3951). In this technology, modeling of grinding conditions is performed in advance by using numerical formulae. Computations of change points of constant infeed speed are made during grinding operation by inputting the actually measured workpiece diameter and other factors into the control unit. The adaptive control grinding, however, has the following disadvantages.
(a) The grinding conditions changes every moment depending on the conditions of workpiece, the conditions of grinding wheel and so on. If an attempt is made to strictly model the grinding conditions, therefore, a huge number of parameters are required, leading to increased computation time. This increase in computation time imposes a limit on sampling intervals and prolongs them. Consequently, this control method cannot follow minute changes in grinding conditions.
(b) Inversely, if the grinding conditions are simplified for ease of modeling, the accuracy of adaption to each workpiece becomes poor.
Another problem with grinding machines is the judgment of time when grinding fluid is changed or replenished.
On machine tools including grinding machines in which a coolant circulates, an operator judges whether the change or makeup of coolant including grinding fluid is necessary. There are many factors the operator must decide; therefore, when a factory is made unmanned, it is difficult to properly change or replenish coolant without waste.
Still another problem with grinding machines is the judgment of timing of truing or dressing of grinding wheels.
To judge the timing of truing or dressing of grinding wheels, the number of workpieces after which truing or dressing becomes required is decided by measuring the grinding accuracy after grinding a certain number of workpieces.
This conventional method takes considerable time for the preliminary work because a number of workpieces must be ground in advance and the grinding accuracy must be measured.
Since the timing of truing or dressing is decided in advance, truing or dressing has to be performed earlier than actually necessary to prevent the grinding accuracy from becoming low. Therefore, truing or dressing is performed when sufficient grinding accuracy Can still be obtained, and dressing is carried out more often than it is actually necessary.